1. I have gone to only one footbal game after I graduated from high school.
2. Despite its cultural importance, the Daily Gazette lost 70 percent of its subscribes since 1920 and, by 1955, was losing as much as $200,000 a year.
首先，此句结构为：Daily Gazette lost it subscribes since 1920 and was losing as much as 200,000 a year. 所以lost 取决于since，was losing取决于a year. a year表示1920后一个持续的状态，所以是was losing. Since说明lost必须是has lost.
3. Untill recently, most people entering politics feel that loss of privacy was a fair price to pay for the chance to participate in policy making.
4. We walked for many hours through the thick forests and over the rocky hills until we had reached the clearing in which we would pitch our tent for the night.
5. If there had been a power failure, the hospital will run on electricity from its own generators, which can operate for 200 hours.
后面说”the hospital will run”，说明power failure没有发生，只是说如果发生，所以应该是if there is 或者是should there be.
但如果是猜测过去是否有可能发生过(例如警探猜测犯罪现场是否有过打斗)，就应该是had there been a power failure, the hospital would have run…
6. By the time the first light of morning showed above the trees, the circus workers had took all of the equipment out of the truck and had begun to erect the tents.
但重要的是by the time说明后面动词应该是past perfect.
7. Recently trollyes have been brought back to solve the problems of congestion caused by the automobile, the very vehicle that causes the trolley’s demise years ago.
1. An agricultural innovator, George Washington Carver aided the economy of the late nineteenth-century South, developed hundreds of uses for crops such as the peanut and sweet potato.
Primary verb是aided。后面应当是by developing才意思对。
1. The director’s insistence that there be adequate stage lighting and professionally installed backdrops in the theater was not obstinate but a determination to provide a safe work environment for the actors and stage crew.